While scientists still aren't absolutely certain what causes Alzheimer's and dementia, "plaques and tangles" are at least a key indicator and maybe a part of the cause. According to the Alzheimer's Association, "plaque" is an abnormal protein that builds up around dead and dying nerve cells. "Tangles" are twisted strands of proteins that coat nerve cells like a blanket.

This new study focused on 44 people ranging in age from 40 to 85 who had reported some mild memory loss but no evidence of dementia. They were give an experimental type of PET (positron emission tomography) scan that can measure plaque and tangles in the brain. The researchers also gathered evidence on the patients lifestyles, their Body Mass Index (BMI), diet and levels of physical activity.

Each of the factors they measured, a healthy BMI (between 18.5 and 24), a fair amount of physical activity and a Mediterranean diet were linked to lower levels of plaque and tangles.

"The fact that we could detect this influence of lifestyle at a molecular level before the beginning of serious memory problems surprised us," said the study's lead author Dr. David Merrill.

Didn't we know this already?

Earlier studies have showed how Alzheimer's can be delayed by living a healthy lifestyle, but this is the first study to who exactly how it works by delaying the growth of plaque and tangles in the brain.

According to Alzheimer's Disease International, an estimated 46 million people around the world had the disease in 2015, and annual costs are around $800 billion annually. That number is expected to rise to 131 million people by 2050.

But as we learn more about the disease it is becoming more clear that keeping active can delay or as Merrill says "prevent Alzheimer's, even before the development of clinically significant dementia."

The next stop Merrill says is to continue imaging the brain to see how other factors like stress reduction and cognitive health might influence Alzheimer's.